The present invention relates to a system for transmitting and receiving binary coded signals representative of letters or patterns superimposed on the television signal during the vertical retrace time intervals, and more particularly a sampling clock reproducing device for a receiver for reproducing good sampling clock pulses when the phase of each bit of said signals is determined independently of the color subcarrier of the television signal.
One of the systems of the type described above is an information transmission system called CEEFAX which has been used in England. The binary coded signals are superimposed on the television signal at the 17H-th and the 18H-th and 330H-th and 331H-th during the vertical retrace intervals (One frame being 625H). One character consists of 8-bits and other control codes also consist of 8-bits. The 8-bit pilot signal called clock run is inserted prior to the binary coded signals. The width of one bit of the clock run signal is one period of 2f.sub.CR (=6.9375 MHz), and this is so set that 6.9375 MHz=444.times.fH which is independent of the color subcarrier f.sub.sc. This phase is arbitrarily selected. The receiver, based on this clock run signal, reproduces sampling clocks for sampling the coded signals. The repetition rate of the binary coded signals (which is defined by the repetition rate of the clock signal) is set to twice as high as the repetition rate of the pulses of the pilot signal. The reason why the repetition rate of the pulses of the pilot signal is set low is that even when there exists waveform distortion the lower the repetition rate the more correctly the receiver may reproduce.